4-Hydroxy-3-methyl-2-2'-propynyl-2-cyclopentenone (hereinafter referred to as propynylcyclopentenolone) is known as one of the important alcohol components in a group of ester compounds called "synthetic pyrethroids" which have excellent insecticidal activities.
For example, a compound of the formula (II) as described below which is an ester of the propynylcyclopentenolone and 2,2,3,3-tetramethylcyclopropanecarboxylic acid is an excellent insecticide having quite strong knockdown and lethal effects (Japanese Published Examined Patent Application No. 50-15843). ##STR2##
There are two kinds of optical isomers in the propynylcyclopentenolone because it has an asymmetric carbon atom in the 4-position thereof, and usually, their activities as esters are greatly different. For example, in the ester represented by the foregoing formula (II), an ester of the (+)-propynylcyclopentenolone has an insecticidal activity several times higher than that of a corresponding ester of the (-)-propynylcyclopentenolone. Thus, there are demanded industrially advantageous technologies of optical resolution of the (.+-.)-propynylcyclopentenolone obtained by the conventional production processes.
As methods for producing optically active propynylcyclopentenolone, a following method has been known; which method comprises converting (.+-.)-propynylcyclopentenolone into a half ester of phthalic acid, reacting this ester with an optically active amine to form diastereomer salts of the optically active propynylcyclopentenolone, isolating and recovering a salt as the amine used and half ester, and then, hydrolyzing the resulting half ester (Japanese Published Unexamined Patent Application No. 56-2929). It is hard to say that this process is satisfactory, however, because it is low in overall yield and requires complicated procedures and expensive optically active reagents.